The formation of cellular polymeric materials by heating a polymeric substance in the presence of certain heat sensitive nitrogen compounds is well known. The characteristics of the expanded product will vary markedly with the specific gas-forming agent used, and selection of the agent for any particular purpose will depend upon the requirements of the intended application. For example, U.S. Pat. No. 2,421,831 discloses diazoaminobenzene as a very effective expanding agent for rubber. This compound, however, suffers from the fact that the material is strongly staining and discoloring and only dark colored cellular rubber or plastic products can be produced when it is used. Freedom from discoloration may be achieved, however, if a non-staining blowing agent such as dinitroso pentamethylenetetraamine is employed. The product is described in U.S. Pat. No. 2,491,709. In this case, however, odorous decomposition products are formed during decomposition of the blowing agent. Employment of the azobis(isobutyronitrile) blowing agent of U.S. Pat. No. 2,484,397 affords a light colored, non-odorous product. Unfortunately a toxic residue is formed from the blowing agent which restricts its application.
Certain organic sulfonhydrazides are free from odor and discoloration features; see, for example, U.S. Pat. No. 2,626,922 and U.S. Pat. No. 2,522,065. These products are widely used as blowing agents, however, their use is limited to applications involving rather restricted temperature ranges. More recently, certain sulfonylcarbazates have been taught to be effective blowing agents; see U.S. Pat. No. 3,925,270 of Hunter. The preparation of carbonylbis(ethyl carbazate) from ethyl carbazate and phosgene is taught in the literature; see J. Ind. Chem. Soc. 10, 685 (1933), no utility is disclosed for that compound.